Check valve appliances are used preferably for infusion instruments in hospitals, whereby the valve appliance is used for the purpose of bringing about an immediate stop to fluid when a dispenser filled with infusion fluid runs dry so that no air gets into the infusion fluid and into the venous system of a patient. A valve appliance for use in an infusion instrument is for example known from the German published application DE 29 19 343 A1, which is equipped with a drip chamber and a float valve, and which prevents the entry of air into the infusion hose when the chamber runs dry, whereby on the exit side in the flexible line leading to the infusion needle a roller clamp is arranged. To prevent a filling of the entire line system with air, a double-seat float valve is used with a float ball. Such floating ball valves, however, do not always respond exactly, so that entry of air into the infusion hose may not be prevented in every case.
A further check valve device is known from the German published application DE 36 32 412 A1, in which a valve is arranged in front of a drip chamber in the direction of flow. A floating ball is adjacent to the channel wall under friction during sealing and cannot prevent air supply with absolute certainty in the corresponding range of motion.
From DE 197 49 562 A1 an infusion instrument is further known which consists of a high suspended container for the infusion fluid as well as an IV stand that can be connected to a throttle container by means of a tribolet tube, an adjustable roller clamp underneath on a flexible inlet tube and an injection needle located at the end of the tube. To prevent the penetration of air into the infusion fluid, in particular at the end of the infusion fluid, in the direction of flow before the drip chamber or at its entrance, a built-in valve is provided that depends upon the static pressure of the infusion fluid flow. However, in practice there is the possibility of interchanging the terminals of the valve through carelessness and thus the function of the valve is no longer guaranteed. This becomes particularly dangerous if air penetrates into the system, which, in case the air penetrates all the way to the veins, can result in an embolism for the patient. It is therefore important that no air mixes in with the infusion fluid, which results in the above mentioned disadvantage. One particular disadvantage is that this aforementioned valve may prevent the penetration of air into the system where there is an excess static pressure at the outlet.
Accordingly, there is a need for a check valve with low opening pressure which can be used for an infusion set and assembly thereof with gravitational pressure and/or pump pressure and which prevents the penetration of air into the system of the infusion set and assembly thereof with high certainty.